This invention relates to a four cycle outboard motor and more particularly to an improved mounting arrangement for the oil pan of such outboard motors.
For a variety of reasons, the two cycle internal combustion engines normally utilize with outboard motors are being replaced with four cycle engines. In spite of their lower specific output, the improved efficiency and lower emission of four cycle engines is causing them to replace two cycle engines for this type of application.
However, four cycle engines present certain additional difficulties in connection with the design and layout of the components for an outboard motor. As is well known in this art, outboard motors provide substantial challenge to the designer because of the compact nature and the desire of maintaining silence and smooth running in such a small package.
Unlike two cycle engines, the four cycle engines generally employ a recirculating lubricating system that requires the provision of a fairly large capacity oil tank. In order to maintain a low center of gravity for the outboard motor and particularly the powerhead portion thereof, it has been the practice to position the oil tank in the upper portion of the drive shaft housing and lower unit. This presents certain problems in connection with exhaust treatment and also with the problem of noise reduction and strength.
Generally, the drive shaft housing is a fairly thin wall casting made from a light metal alloy. Also, the oil pan should have a relatively thin wall construction and is generally placed in spaced relationship with the interior surface of the drive shaft housing. This provides some cavity around the oil pan which can be utilized for idle exhaust gas flow. However, the spacing of the walls can give rise to certain problems in connection with noise generation and loss of rigidity.
Also, there is a problem in connection with designing the oil pan and drive shaft housing in such a way that the oil pan can be conveniently drained for servicing without removing it from an associated watercraft. The prior art type of constructions have provided oil drains that extends through an inclined lower wall of the oil pan. Generally, an elastic seal is provided between this drain and the drive shaft housing and this is the only true direct connection between the drive shaft housing and the oil pan. Thus, the aforenoted problems exist.
Although the problems attendant with the prior art constructions have been described above, it is believed that a descriptive figure will be helpful to permit those skilled in the art to understand the invention. FIG. 1, therefore, is a partial view of a prior art type of outboard motor, indicated generally by the reference numeral 31 and shows primarily the oil pan arrangement and the association of the oil pan with the exhaust system.
The conventional outboard motor 31 includes a power head, which is not shown but which extends above an exhaust guide 32 that is fixed and supported in a suitable manner across the upper end of a drive shaft housing unit, indicated generally by the reference numeral 33. This exhaust guide 32 has an exhaust passage 34 that communicates with the discharge end of an exhaust manifold of a four cycle internal combustion engine which is supported in the aforenoted power head and which is not illustrated.
An exhaust pipe 35 has a flanged portion 36 that is affixed to the underside of the exhaust guide 32 by threaded fasteners 37. The exhaust pipe 35 has an inlet end that is configured to be complementary to the exhaust guide exhaust passage 34 so as to collect the exhaust gases and deliver them downwardly to an expansion chamber 38 that is formed in the drive shaft housing lower unit 33.
The engine, which as has been noted is not shown, is of the four-cycle type. Therefore, there is provided an oil pan or oil reservoir 39 that is mounted on the underside of the exhaust guide 32 in a suitable manner and which contains lubricant for the engine.
This oil pan 39 is formed with an oil drain arrangement 41 that includes a drain plug 42 that is tapped into a threaded opening in an inclined lower wall 40 of the oil pan 39. A sealing gasket 43 surrounds the drain plug 42 and the drain plug is accessible through an access opening 44 formed in the drive shaft housing 33. This permits the lubricant to be drained from the oil pan 39 without its removal from the outboard motor 31. The drain plug 42 extends through an inner wall 45 of the drive shaft housing 33 and which is surrounded by a cowling portion 46.
The sealing gasket 43 provides the only direct support between the oil pan 39 and the drive shaft housing 33 and thus the aforenoted problems remain unsolved.
It should be seen that the oil pan 39 is formed with an inner wall 47 that surrounds the exhaust pipe 35. The lower wall of the oil pan 39 terminates well above the lower end of the exhaust pipe 35. This means that when the outboard motor 31 is operating at idle or trolling condition, the end of the exhaust pipe 35 may be quite close to the water level. If misfiring occurs, either accidentally or intentionally to control the speed of the engine, negative pressure pulses may exist in the exhaust pipe 35. The water may then be drawn upwardly into the exhaust system when this occurs, obviously not a desirable condition.
The exhaust gases from the expansion chamber 38 are discharged to the atmosphere through a conventional underwater high-speed exhaust gas discharge. This may include a known type of through-the-hub underwater discharge.
Under low speed and low loads, however, the exhaust gases are delivered to the atmosphere through an above-the-water exhaust gas discharge. This is done because the back pressure would be too high to permit the discharge of the exhaust gases through the main exhaust system.
This idle discharge system includes a restricted passage 48 that is formed in the upper part of the exhaust pipe 35. The exhaust gases pass through this opening 48 and are deflected away from the oil pan wall 47 by a baffle 49. The exhaust gases then flow downwardly as indicated by the arrow 51 to an area between the outer surface of the oil pan 39 and across the inclined wall 40 and an inner surface wall 52 of the drive shaft housing 45. These exhaust gases then flow upwardly and through a restricted passageway 53 in the wall 52 as shown by the arrow 54. The exhaust gases then pass into an expansion chamber 55 formed by a further wall and which then can flow to the atmosphere through an idle discharge passage 56 formed in the drive shaft housing 33 in the direction of the arrow 57.
A water drain 58 is formed at the lower end of the expansion chamber 55 so that water that may be entrapped with the exhaust gases 10 drains back to the body of water in which the watercraft is operating.
The engine, which is not shown, has a water cooling system that includes a cooling jacket through which coolant is circulated by a water pump in a known manner. This coolant is then discharged at least in part to a cooling jacket 59 formed in the exhaust guide 32 around the exhaust passage 34. This water then fills a weir type device surrounding the oil pan 39 for its cooling and is discharged downwardly through a drain passage 61 for discharge through the lower unit in a known manner.